Boiler fault codes and problem checker

What a code or problem means, what you can safely check, and when to ring.

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Pick what your boiler's doing

No heating and no hot waterOther problems
What it usually means
No heating and no hot water usually means the boiler has stopped. The cause may be no power, no gas, low pressure, or a fault it has shut down for. In a frost, a frozen condensate pipe is a common cause.
Try this first
1. Power: is the display lit? Check the switch by the boiler and the fuse box.
2. Gas: does the hob light? On a prepayment meter, check the credit, then reset the boiler. Smell gas? Open the gold "Smell gas?" bar.
3. Controls: heating on, timer on, thermostat turned up.
4. Pressure: about 1 to 1.5 bar when cold. Below 1, top it up as your user guide shows.
Then ring us
Still nothing, or a code stays on? Ring us now. We'll ask what the display and the gauge show.
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Where to start when the heating and hot water stop
Pressure low or on zeroOther problems
What it usually means
Low pressure usually means water has left the heating system, through a small leak, the relief valve, or bleeding radiators. An expansion vessel that has lost its charge can cause it too.
Try this first
1. Look for leaks: drips, damp or rust under the radiators, at their valves and along the pipes you can see.
2. Check the pipe outside: the pipe from the boiler through the wall should be dry. Wet means the relief valve has let water out.
3. Top up: boiler off and cool, to about 1 to 1.5 bar, with the filling loop as your user guide shows. Close both its valves fully. No steps in your guide? Ring us.
4. Keep an eye on it: topping up once or twice a year is normal. More often can mean a small leak.
Then ring us
Pressure dropping again, or on zero? Ring us now. The makers advise against topping up again and again. We'll ask what the gauge reads and how often you top it up.
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A boiler that keeps losing pressure, and what it usually means
Pressure too high or pipe dripping outsideOther problems
What it usually means
High pressure, over about 2.5 bar with the boiler cool, usually means too much water in the system. The usual causes are a filling loop left open, a top-up taken too far, or an expansion vessel that has lost its air. The relief valve then lets water out through the pipe outside.
Try this first
1. Let it cool: then read the gauge again. Pressure rises a little as the water heats, which is normal.
2. Check the filling loop: both its valves should be fully closed.
3. Bleed a radiator: heating off and radiators cool, a cloth under the valve, a quarter turn at most. Stop at about 1 to 1.5 bar.
Then ring us
Pressure high again, or the pipe outside still dripping? Ring us now. We'll ask what the gauge reads cold and hot.
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What rising or falling pressure usually means
Radiators cold at the bottomOther problems
What it usually means
Radiators cold at the bottom usually have sludge settled inside. It's rust from the radiators and pipes, and limescale in a hard water area. More than one like it means sludge through the system.
Try this first
1. Count them: heating on, feel each radiator and note which are cold at the bottom.
2. Leave the radiator key: bleeding lets out air at the top, not sludge at the bottom.
3. Think back: black water when you last bled a radiator points to sludge too.
Then ring us
More than one cold at the bottom? Ring us. A power flush clears the sludge from the radiators, the pipes and the boiler. We'll ask how many are cold.
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Power flushing: when it helps
A radiator cold at the topOther problems
What it usually means
A radiator cold at the top has air trapped in it. Bleeding it lets the air out.
Try this first
1. Heating off: let the radiators cool, about an hour.
2. Bleed it: a cloth under the valve at the top, then a quarter to half a turn anticlockwise with the radiator key. Close it when water comes.
3. Check the pressure: bleeding lowers it. Top up to about 1 to 1.5 bar cold, as your user guide shows.
4. Heating on: feel the radiator again.
Then ring us
Still cold, or needs bleeding again and again? Ring us. We'll ask how often you bleed it.
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Radiators cold at the top, and bleeding them step by step
Water leaking from the boilerOther problems
What it usually means
A leaking boiler usually means the pressure is too high, and the relief valve is letting water out. Otherwise, a joint or seal inside may have started to leak. In a frost, a frozen condensate pipe can back water up.
Try this first
1. Catch the water: a bucket or bowl, with towels around it.
2. Switch the boiler off at its switch.
3. A lot of water? Turn it off at the stopcock.
4. Look, don't open: see where it's coming from without taking the casing off, and read the gauge.
Then ring us
Any leak, even a small drip? Ring us straight away, as water can upset the electrics. We'll ask where the water is and what the gauge reads.
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What to do about a leaking boiler
Banging, kettling or gurglingOther problems
What it usually means
Gurgling is usually air in the system, or a frozen condensate pipe in a frost. Banging, or a whistle like a kettle, is usually kettling. That's water boiling inside the boiler, because limescale, sludge, the pump or a thermostat is holding it up.
Try this first
1. Gurgling: bleed any radiators cold at the top, then check the pressure.
2. In a frost: check the condensate pipe outside, and thaw it if you can reach it at ground level.
3. Note when: a bang as a tap goes on or off is often the pipes, not the boiler.
Then ring us
Banging, kettling, or gurgling that bleeding doesn't stop? Ring us. The fix is inside the boiler. We'll ask what the noise sounds like and when it comes.
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What each boiler noise means
Won't fire up or keeps locking outOther problems
What it usually means
A boiler that won't fire up hasn't been asked to light, or has tried, failed and locked out for safety. It usually shows a code or a light.
Try this first
1. Power and controls: display lit, switch on, nothing tripped, thermostat turned up.
2. Gas: does the hob light? Credit on a prepayment meter? Smell gas? Open the gold "Smell gas?" bar.
3. In a frost: check the condensate pipe outside for ice.
4. Reset once, as the user guide shows, once the cause is put right.
Then ring us
Locked out again after one reset, or the same code keeps coming back? Ring us now, as resetting again and again can damage the boiler. We'll ask what the display shows.
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Resetting a boiler once, and when to stop
Condensate pipe frozenOther problems
What it usually means
A frozen condensate pipe stops a condensing boiler in a hard frost. The plastic pipe that takes its waste water outside freezes, and the boiler shuts down, often gurgling and showing a code.
Try this first
1. Find it: follow the white plastic pipe outside. It usually freezes at the end, or at a bend.
2. Thaw it: at ground level, pour warm water over it, never boiling, or hold a hot water bottle against it.
3. Mind your step: the water can freeze on the ground.
4. Reset the boiler as its user guide shows.
Then ring us
Pipe high up, won't thaw, keeps freezing, or the boiler still won't start? Ring us. Never climb to reach it.
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How to thaw a frozen condensate pipe safely
A smell of gasOther problems
What it usually means
A smell of gas can mean a gas leak. Ring the National Gas Emergency Service first, not us: 0800 111 999, free, 24 hours a day. Do the same if a carbon monoxide alarm sounds.
Do this now
1. Open the doors and windows.
2. Turn the gas off at the meter's handle, unless the meter is in a cellar or basement.
3. No switches, no flames: don't touch anything electrical. No smoking, no matches.
4. Get out, and ring 0800 111 999 from outside.
Then ring us
Once the emergency service has made it safe, ring us. The boiler stays off until a Gas Safe registered engineer has checked it, and every engineer we send is Gas Safe registered. Don't turn the gas back on yourself.
Ring 0800 111 999: free, 24 hours a day Call us now
Gas safety at home, and what to do about a gas smell

Not on the list? Ring us and say what the boiler's doing: we'll ask the rest.Call us now

24 makes covered
From their manuals
Safe checks
When to ring

Makes we repair

More makes

Common fault codes, explained in full

Sixteen common codes are explained in full, and so are Worcester Bosch's codes. Each says what the code means on every make that shows it, what you can safely check, and when to ring.

F28Vaillant and Glow-worm: the boiler tried to light and found no flame.
F22Vaillant and Glow-worm: the water pressure is too low.
F75Vaillant and Glow-worm: the pressure didn't rise when the pump started.
L2Ideal: the boiler tried to light five times, then locked out.
F1Ideal: the water pressure is too low. An older Glow-worm means something else.
F2Ideal: the flame went out. Viessmann: the overheat cut-out has tripped.
E119Baxi and Potterton: the water pressure has dropped below 0.5 bar.
E133Baxi and Potterton: the gas supply was cut, or the flame didn't light.
F29Vaillant and Glow-worm: the flame went out and the boiler couldn't relight.
F83Vaillant and Glow-worm: the boiler lit, but the water barely warmed.
F62Vaillant and Glow-worm: the flame went out late as the gas valve shut.
F54Vaillant: too little gas reached the boiler as it started.
E125Baxi and Potterton: the water isn't circulating properly.
F3Ideal: a fan fault. Viessmann: a flame seen before the burner lit.
A21Worcester Bosch: a code from the heating controls, often a lost signal.
Alpha E01Alpha: the boiler tried to light and found no flame.
Worcester Bosch codesThe Greenstar's codes and lights, and what each one means.

Codes by make

Every make we repair has its codes set out in full, the main ones explained and a list of the rest. Pick your boiler's maker.

Not sure of your boiler's make? How to find it.

Is your boiler from a make no longer sold? We explain the codes, lights and faults of Halstead, Johnson & Starley, Malvern and Myson boilers.

Every other code, make by make

Each make's main codes are listed below, every one linked to where it is explained. Each make ends with a link to its full list for the rest. Open your boiler's make.

Vaillant: F. and two or three figures

Vaillant boilers show F. and two figures, such as F.28. The current ecoTEC plus, from 2023, shows three, such as F.028, with the same meaning. Some codes on an older ecoTEC, turboMAX or ecoMAX mean something else. Which Vaillant boiler shows which kind of code.

F.23 (F.023): the water isn't moving round fast enough
F.20 (F.020): the overheat cut-out has stopped the burner
F.24 (F.024): the temperature rose too fast
F.27 (F.027): a flame where there shouldn't be one
F.76 (F.076): the main heat exchanger's overheat protection
F.28: the boiler tried to light and found no flame
F.29 (F.029): the flame went out and wouldn't relight
F.22: the water pressure is too low
F.75: the pressure doesn't rise when the pump starts
F.54: not enough gas pressure at start-up
F.62 (F.062): the flame went out late after the gas valve shut
F.83 (F.083): the burner lit, but the water barely warmed

The rest of the Vaillant codes are in one list on the Vaillant page.

An older Vaillant turboMAX's codes, model by model.

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Worcester Bosch: numbers, letters or a blue light

Worcester Bosch Greenstar boilers show a fault in one of five ways, by age. Some show a number with a line of text, or a number with an H. Some show two characters with a three-figure number, such as EA 227, and some two characters alone. Others flash a blue light in a pattern. Which Worcester Bosch boiler shows which kind of code.

EA 227 (Greenstar i System, Si and CDi Compact) or 227 (8000+, 8000 Life, 4000, 2000, 1000): no flame
EA 229 (Greenstar i System, Si and CDi Compact) or 229 (8000+, 8000 Life, 2000, 1000): the flame went out while the boiler was running
E9 224 (Greenstar i System, Si and CDi Compact) or 224 (8000+, 8000 Life, 4000, 2000, 1000): an overheat safety device has tripped
1017 (Greenstar 8000+, 8000 Life, 4000): the system pressure is low
2971 (Greenstar 8000+, 8000 Life, 4000, 2000): the pressure is too low and the boiler has stopped
A1 281 (Greenstar i System, Si and CDi Compact) or 281 (8000+, 8000 Life, 4000, 2000): the pump
D5 (Highflow, FS CDi Regular, 2012 Greenstar 24/28): a different fault on each range
C6 (Greenstar i System, Si and CDi Compact, CDi Classic, Highflow, FS CDi, 2012 24/28): the fan
2980 (Greenstar 8000+, 4000, 1000): a super lock-out
A21: a code from the Greenstar heating controls, often a lost signal

An older Worcester 24i's lights and faults.

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Baxi: E and a number, or numbers with dots

Baxi's current Combi 2 and System 2 show a letter and numbers with dots, such as A.02.06. Older Baxi boilers show E and a number, such as E133, and the Heat boilers a light. The same number can mean something else on another range. Which Baxi boiler shows which kind of code.

E110: the boiler has overheated
E160: a fan fault
A.02.06: a low-pressure warning, and the boiler keeps running
H.02.07: the water pressure is too low, and the boiler has stopped
E118: the water pressure is too low, under 0.5 bar
E.04.10: the burner didn't light after 4 tries
E.01.17: no water moving, and the boiler has locked out
H.01.18: no water moving, and the boiler waits
E119: the water pressure has dropped below 0.5 bar
E125: the heating water isn't moving round properly
E133: the gas supply was interrupted, or the flame didn't light

The rest of the Baxi codes are in one list on the Baxi page.

An older Baxi Duo-tec's codes, edition by edition.

An older Baxi Solo's lights and faults.

A Baxi Combi 80e or 105e's lights and faults.

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Ideal: a letter and a number, or words

Ideal's Logic+, Logic Max and Vogue name the fault in words. The Logic Combi2 and i-mini show a letter and two figures, such as L 02. The ESP1, the Exclusive2 and older Logic boilers show a letter and one figure, such as L2, with the same meaning. Which Ideal boiler shows which kind of code.

L1 (Overheat): too hot, or no water moving
LC (Too Many Restarts): five restarts in 15 minutes
L6 (Flame On Before Gas On): a flame before the gas opens
L8 (and L 08): the Restart button, the main board or the fan, by range
F4 and F5 (also L4 and L5): the flow and return sensors
F7 (Low Mains Voltage): too little electricity
L2 (Ignition Lockout): the boiler tried to light five times and failed
F1 (Low Water Pressure): the pressure is too low for the boiler to run
F2 (Flame Loss): the flame went out while the boiler was running
F3 (Fan Fault): the fan isn't running as the main board expects

The rest of the Ideal codes are in one list on the Ideal page.

An older Ideal Mexico's codes.

An older Ideal Classic's faults.

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Viessmann: two characters, or a number

Viessmann's Vitodens boilers before the One Base show two characters beside a fault symbol, such as F4. The current One Base boilers show a number, and the same characters mean other things there. Which Viessmann boiler shows which kind of code.

F4: no flame signal
EE: no flame as the burner starts, on a 200-W B2HB
F8: the gas valve closes too late, or won't close on a 200-W B2HB
F9: the fan is too slow at start-up
FA: the fan doesn't come to rest, or on a 200-W B2HB doesn't reach its speed
FC, Fd and FF: the control unit, or on a 200-W B2HB the gas valve or the flue (FC)
F2: the overheat cut-out has tripped
F3: a flame signal before the burner lights

The rest of the Viessmann codes are in one list on the Viessmann page.

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Glow-worm: F. and two figures

Glow-worm's current boilers show F. and two figures, such as F.28, and the Betacom2 and Ultracom2 drop the dot. The Flexicom, the first Ultracom and older boilers flash F and a number that means something else. On those, F1 is an ignition fault. Which Glow-worm boiler shows which kind of code.

F.20: the overheat cut-out has shut the boiler off
F.23: the flow and return are too far apart
F.24: the temperature rises too fast
F.27: a flame signal with the burner off
F.32: fan fault
F.28: the boiler tried to light and failed
F.29: the flame went out and wouldn't relight
F.22: there isn't enough water in the boiler
F.75: a pressure or pump fault found as the pump starts
F.62: the flame went out late after the gas valve shut
F.83: the burner lit, but the water barely warmed
F1 on an older Flexicom, Ultracom or cxi: an ignition fault
F3 on an older cxi, Flexicom or Ultracom: the fan couldn't reach its lighting speed

The rest of the Glow-worm codes are in one list on the Glow-worm page.

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Potterton: E and a number, or a light

Potterton boilers with a display show E and a number, such as E133, which a two-figure display splits into E1 and 33. The Titanium Heat uses a coloured light, and the Performa and Suprima use lights. Low pressure is E119 on the Promax, Titanium and Gold, and E118 on the Assure and Ultra. Which Potterton boiler shows which kind of code.

A Potterton boiler flashing a green light: which boiler is it?
E118: the water pressure is too low, on the Assure and the Promax Ultra
E110: the safety thermostat has tripped
E130: the flue has overheated
E160: a fan fault
E28: the flue sensor, or a blocked flue or condensate pipe
E20 and E50: the heating and hot water sensors
E119: the water pressure has dropped below 0.5 bar
E125: the heating water isn't moving round as it should
E133: the gas supply was interrupted, or the flame didn't light

The rest of the Potterton codes are in one list on the Potterton page.

A Potterton Suprima's lights and faults.

An older Potterton Profile's faults.

An older Potterton Netaheat's faults.

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Alpha: E and a number, or lights

Alpha boilers give each fault a number, written E01, E10 and so on, on a screen. The older CD combis show a pattern of four lights. Which Alpha boiler shows which kind of code.

E10: the system pressure is too low
E02: the overheat sensor has tripped
E03: the flue gas is too hot
E16: a fan fault
E38 and E43: the flame lit, then went out
E01: the boiler tried to light and found no flame

The rest of the Alpha codes are in one list on the Alpha page.

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Vokera: an A, E or AL code, or lights

Vokera's codes have changed over the years. The older Compact A, Vision, Unica i and Mynute i show A01 to A11. The Vibe MAX and Easi-Heat i show A10 and up. The Synergy, Pinnacle and Evolve show E codes, and older boilers show AL codes or lights. Which Vokera boiler shows which kind of code.

A01: the boiler didn't light
A02: the limit thermostat has tripped
A03: no signal from the fan
A04: the system pressure is too low
A06 to A09: a sensor fault
A11: a flame where there shouldn't be one

The rest of the Vokera codes are in one list on the Vokera page.

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Ariston: three figures, sometimes in words

Ariston's E-Combi ONE and Clas ONE flash three figures, and Err with the code when they lock out. The Genus ONE+ and Alteas ONE+ print the code with its meaning in words. The first figure says where the fault is. Which Ariston boiler shows which kind of code.

108: the pressure is low, and the system needs filling
501: no flame, and the boiler has locked out
101: the heating water has overheated
109: the pressure is too high
304: the reset key was pressed too many times
502: a flame sensed with the gas valve closed

The rest of the Ariston codes are in one list on the Ariston page.

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Keston: words, a code or a light

Keston's Combi 2 and System 2 name the fault in words, as Ideal's Logic+ Combi2 does. The System S30 shows a letter and a number, such as L2, and the Heat 2 shows Fault and a number. Which Keston boiler shows which kind of code.

Ignition Lockout (L2 on a System S30)
Flame Loss (F2 on a System S30)
Low Water Pressure (F1 on a System S30)
Overheat (L1 on a System S30)
No Water Flow (Combi 2 and System 2)
Too Many Restarts (LC on a System S30)
L2: the boiler tried to light and locked out
F1: the water pressure is too low for the boiler to run
F2: the flame went out while the boiler was running

The rest of the Keston codes are in one list on the Keston page.

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Biasi: Er, E or A and two figures, or lights

Biasi's Advance Plus shows Er and two figures. The Antares, RinNova and Dina number their codes their own way, and the Riva uses three lights. The same number can mean different things on each range. Which Biasi boiler shows which kind of code.

Er 01: the burner didn't light (Advance Plus)
Er 02: the overheat thermostat has tripped (Advance Plus)
Er 04: no water, or no flow (Advance Plus)
Er 05: a fault in the fan's control (Advance Plus)
Er 14: the pump, or water above 105°C (Advance Plus)
Er 25: a flame detection error (Advance Plus)

The rest of the Biasi codes are in one list on the Biasi page.

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ATAG: three characters, such as 501 or 1P4

ATAG boilers from 2019 show three characters, such as 501 or 1P4, with a spanner or a bell. Boilers from 2015 to 2018 show two or three figures, and a few of those mean something else. Which ATAG boiler shows which kind of code.

108 and 1P4: the pressure is too low
501: no flame detected
101: an overheat
103 to 107: the flow checks have failed
109: the pressure is too high
304: too many resets
118 and 133: low pressure or a sensor fault on 118, by the boiler's age, and no flame on 133

The rest of the ATAG codes are in one list on the ATAG page.

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Navien: E and three figures

Navien's NCB700 ON, NCB500 ON and NCB300 combis and NCB500 System show E and three figures, such as E302 for low pressure. The older NCB-CE shows a three-figure code in turn with an Error sign. The lists differ a little between ranges. Which Navien boiler shows which kind of code.

E003: the boiler didn't light
E012: the flame went out while running
E302: the water pressure is too low
E001: the heat exchanger is too hot
E016: the heat exchanger's overheat cut-out has tripped
E030: the flue gases are too hot
E109: the fan
E110: the flue or condensate is blocked (NCB700 and NCB-CE)
E205: the heating flow sensor

The rest of the Navien codes are in one list on the Navien page.

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Intergas: F and three figures, or a number and a red light

Intergas's Xclusive and Xtreme show F and three figures on a touch screen, such as F004. The HRE, ECO RF and Rapid show a number on the main display, with a red light flashing above the reset key. The small service display's numbers are what the boiler is doing, not faults. Which Intergas boiler shows which kind of code.

F004: no flame when lighting
F005: the flame was lost while running
F001: too hot while heating
F003: the flue gases are too hot
F008: the fan speed is wrong
F018: the flue or air supply is blocked
F010 and F011: the heat exchanger sensor

The rest of the Intergas codes are in one list on the Intergas page.

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Main: a number, an E code or a light

Main Eco Compact boilers, now sold as the Baxi MainEco Compact, flash a number, such as 133, with an R when you may reset it. The older Eco Elite shows the same faults with an E, such as E133, and the Eco Compact Heat a light. Low pressure is 118 on one and E119 on the other. Which Main boiler shows which kind of code.

133 or E133: the gas supply, the spark or the flame failed
118 (Eco Compact) or E119 (Eco Elite): the water pressure is too low
110 or E110: the boiler has overheated
125 or E125: the water isn't moving round well enough
128: the flame went out while the boiler was running
160 or E160: the fan or its wiring

The rest of the Main codes are in one list on the Main page.

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Ferroli: A or F and two figures

Ferroli's Bluehelix boilers show A codes and F codes, such as A01 or F37. An A code locks the boiler out until it is reset, and an F code clears when the cause does. The Modena and T-One use the same letters, and some numbers mean something else on each range. Which Ferroli boiler shows which kind of code.

A01: the burner didn't light
F1 (01) on an Optimax 25 S: the burner didn't light
A06: the flame went out after lighting
F37 and F40: the water pressure is too low, or too high
A08, A09 and A03: the boiler overheated
F05 and A05 (F15 on a Modena): the fan isn't running at the right speed
F10: the flow temperature sensor has failed
A14 and A07 (A04 on a Modena): the flue gases ran too hot

The rest of the Ferroli codes are in one list on the Ferroli page.

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Ravenheat: two figures and an E, a number, or a light

Ravenheat's CS80, CS90 and HE boilers show two figures and an E, such as 01E. The CSI 120, CSI 150 and HE 42 show a number alone, such as 01 or 28, which doesn't match the E codes. Older boilers show a red light. Which Ravenheat boiler shows which kind of code.

01E (01 on the boilers that show a number alone): the boiler couldn't light, and has locked out
08E (28 on the boilers that show a number alone): the water pressure is too low
12E: too many resets
06E, 09E, 21E and 29E (04 on the boilers that show a number alone): the boiler has overheated. 02E means the water isn't moving
22E and 23E (30 and 31 on a WH 100 or WH 130): the flue is too hot, or its sensor has failed
25E: the main heat exchanger has frozen

The rest of the Ravenheat codes are in one list on the Ravenheat page.

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Heatline: F and one or two figures, or lights

Heatline's Capriz 2 shows F. and two figures, such as F.28, and the CaprizPlus and Monza the same without the dot. The Solaris, Sargon and Vizo Plus show F and one figure, and older boilers show flashing lights. The same number can mean something else on an older one. Which Heatline boiler shows which kind of code.

F28 (F.28): the boiler tried to light and failed
F29: the flame went out while running
F22 (F.22): the water pressure is too low
F20: the boiler has overheated
F32: the fan or the air pressure
F00, F01, F10 and F11: a temperature sensor

The rest of the Heatline codes are in one list on the Heatline page.

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Sime: ALL or AL and two figures

Sime's Edea shows ALL and two figures, such as ALL 02, and the Giulia AL with the same numbers. On the Edea T system boiler two of them swap, and older Murelle boilers have a list of their own. Which Sime boiler shows which kind of code.

ALL 02 (AL 02): the water pressure is too low
ALL 06 (AL 06) and ALL 41: no flame, or the flame keeps going out
ALL 07 (AL 07): the overheat thermostat has tripped
ALL 09 (AL 09): no water moving round the heating
ALL 15 (AL 15): a fan fault
ALL 18: condensate is backing up (Edea)
ALL 28 (AL 28): too many resets in a row

The rest of the Sime codes are in one list on the Sime page.

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Remeha: e and a number, or a letter and four figures

Remeha's Avanta boilers show e and a number, taking turns on the display, so e then 2 is e2. The Avanta Plus added e9 for low pressure. Newer Remeha boilers, such as the Quinta Ace, show codes like E.04.10. Which Remeha boiler shows which kind of code.

e4: the burner didn't light
e5: the flame went out
e9: the water pressure is too low
e1: the boiler has overheated
e7 and e10: no water, or no flow
e8: a fan fault
e0: a temperature sensor fault

The rest of the Remeha codes are in one list on the Remeha page.

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Megaflo: E and three figures, on the system boilers

Megaflo is two products. Megaflo unvented cylinders show no code. Baxi's Megaflo system boilers show E and three figures, such as E118 for low water pressure, where many Baxi boilers show E119. Which Megaflo boiler shows which kind of code.

E118 (not E119): the water pressure is too low
E133: the gas supply was interrupted, or the flame didn't light or wasn't detected
E110: the safety thermostat has tripped, from overheating
E125: the heating water isn't circulating
E117: the water pressure is too high
E128: the flame went out while the boiler was running
E160: the fan or its wiring

The rest of the Megaflo codes are in one list on the Megaflo page.

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Powermax: a letter and a number, or lights

The Potterton Powermax HE's red display shows A for a lockout, E for an error and P for the heating pressure, such as A 01. The older Range Powermax shows its faults with lights. Which Powermax boiler shows which kind of code.

A 01: the burner did not light (Powermax HE)
A 15 or P 0.1 to 0.4: the heating pressure is lost (Powermax HE)
P 3.0 to 3.5, or E 01: the heating pressure is too high (Powermax HE)
A 03 and E 03: an overheat lock-out, the flow too hot (Powermax HE)
A 40 (A 02 in the user's instructions): a system response fault (Powermax HE)
E 20 and A 20: a flame sensed with the gas valve closed (Powermax HE)
Red light: the Range Powermax's red lock-out light

The rest of the Powermax codes are in one list on the Powermax page.

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Geminox: three figures, shown in two parts

Geminox boilers show a code of three figures, such as 133. The THI's two-digit display shows it in two parts, a 1 and then 33. The same number can mean something else on the THRs. Which Geminox boiler shows which kind of code.

118 (323 on a THRs): the water pressure is too low
117: the water pressure is too high
133: no flame, so the boiler has locked out (E 1, then 33, on a ZEM)
153: the boiler is locked
110: the overheat safety has tripped (on a THRs, the underfloor limiter)
128: the flame went out while the boiler was running
160: the fan isn't reaching its minimum speed

The rest of the Geminox codes are in one list on the Geminox page.

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How to find your boiler's make and model

A boiler's make and model are on its casing, where you can read them without opening it. The maker's name is on the front. The model, often with the serial number, is on a data plate or label. Here is where the makers say to look:

Vaillant and Glow-worm: the data plate, under the boiler.
Worcester Bosch: the front of the boiler, or the data label inside its door.
Baxi: a pull-out tab under the front of the boiler, for the serial number.
Potterton: the information label at the front.
Biasi and ATAG: a sticker or the flap at the front.

Never take the case off to look. If you can't find the model, ring us anyway. We'll ask what the display shows, and the code and the way it shows often name the range.

What a fault code can and can't tell you

A fault code tells you what the boiler's sensors found, not which part has failed. F28, for one, means the boiler couldn't light. Vaillant's manual lists five groups of causes behind it, from the gas supply to the control board. The code shows an engineer where to start, and finding the cause is the work.

The same code can mean different things on different boilers. F1 is low water pressure on an Ideal, and an ignition fault on an older Glow-worm. Low pressure is E119 on a Potterton Promax, and E118 on a Potterton Assure. Read the make and model before the code, and we'll ask for both when you ring.

A lockout is the boiler keeping you safe. When it finds a fault it shouldn't run with, the boiler stops and waits for a reset. Some codes clear by themselves once the cause has gone. On the current Vaillant ecoTEC plus, low pressure clears once the system is topped up.

Worth knowing

On a Baxi Main Eco or a Potterton Assure, an R beside the code means you may reset it at home. A spanner means it needs an engineer.

Do you cover my part of London?

Yes, we fix boiler faults all over Greater London, in every borough north and south of the Thames. Pick your side of the river to see the areas.

Every area we cover, borough by borough.

North of the river

Every borough north of the Thames: Barnet and Enfield at the top, Hillingdon in the west, Havering in the east, and central London in between.

South of the river

Every borough south of the Thames: Richmond and Kingston in the west, Bexley in the east, and down through Croydon to Sutton and Bromley.

All the areas we cover

Questions about boiler fault codes

Can I clear a fault code myself?

A fault code can be cleared at home when the maker's user guide says so. It might be a reset, or topping up the pressure where the guide shows how. The guides set a limit on resets. Most Vaillant and Glow-worm boilers allow three, and an Ideal locks out with LC after five restarts in 15 minutes. If the code comes back, the fault needs an engineer.

Is it safe to reset the boiler?

A reset is safe to try when the user guide allows it and you can't smell gas. If you smell gas, don't reset anything. Open the gold "Smell gas?" bar on this page for the free emergency number. Never open the boiler's case to reach a reset or a part.

Why does the code keep coming back?

A code that keeps coming back means its cause is still there. The reset clears the display, not the fault. Some causes come and go, such as a gas supply that drops or a condensate pipe that refreezes overnight. That's why a code can clear and return. An engineer tests each cause in turn.

Which codes mean the boiler must stay off?

Any code that comes back after the resets the guide allows means the boiler should stay off until an engineer has looked at it. The same goes for any fault with a smell of gas. Some makers mark the codes that need an engineer. There's a spanner on a Baxi Main Eco or a Potterton Assure, and an engineer symbol on a Biasi Advance Plus. Vaillant's manuals say a fault such as F.27 shouldn't be reset at all.

How much does it cost to fix a fault code?

The cost of fixing a fault depends on its cause and the part it needs, if any. The rate is agreed on the call, before an engineer comes, and no work is done until you say yes. How our rates work.

Don't know what has failed? You don't have to.Ring and say what you can see or hear. Finding the fault is our job.

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A real person answers and gives you the rate on the call. No work starts until you say yes, and repairs are guaranteed for 12 months: parts, labour and any return visit.